Define __ANDROID_VENDOR_API__

cc modules can use __ANDROID_VENDOR_API__ to read BOARD_API_LEVEL
that is the API level of the vendor surface.

Bug: 313822931
Test: check ninja commands to have -D__ANDROID_VENDOR_API__=<version>
Change-Id: Iceb5918cbfce0f24929d02d7e3caf1e9942b88e8

rust/bindgen.go

@@ -174,6 +174,15 @@ func (b *bindgenDecorator) GenerateSource(ctx ModuleContext, deps PathDeps) andr
 		cflags = append(cflags, "-D__ANDROID_VNDK__")
 		if ctx.RustModule().InVendor() {
 			cflags = append(cflags, "-D__ANDROID_VENDOR__")
+
+			vendorApiLevel := ctx.Config().VendorApiLevel()
+			if vendorApiLevel == "" {
+				// TODO(b/314036847): This is a fallback for UDC targets.
+				// This must be a build failure when UDC is no longer built
+				// from this source tree.
+				vendorApiLevel = ctx.Config().PlatformSdkVersion().String()
+			}
+			cflags = append(cflags, "-D__ANDROID_VENDOR_API__="+vendorApiLevel)
 		} else if ctx.RustModule().InProduct() {
 			cflags = append(cflags, "-D__ANDROID_PRODUCT__")
 		}